High-power light at visible and near visible wavelengths is highly desirable in many applications. In medical applications, specific wavelengths are utilized to affect specific tissues. In the display industry, large displays and projection systems utilize red, green, and blue colors to derive the full observable color spectrum. Yellow lasers (e.g., 589 nm) are particularly useful for guide-star applications in correcting atmospheric distortions in ground-based extra-terrestrial imaging.
Generating power levels above 1 watt at arbitrary wavelengths has proven to be challenging, especially with good beam quality (M2˜1). GaN-based diode lasers can access visible and near-visible wavelengths, but the available output power is generally limited to the sub-watt level. Various gas and liquid (i.e., dye) lasers have similar performance, but are also plagued with efficiency and reliability issues, as well as significant system complexity. Despite their high reliability, solid-state and fiber lasers cannot readily access such wavelengths. One common technique used to obtain visible light is by frequency shifting via parametric processes, such as difference frequency generation, sum frequency generation, and second harmonic generation. While in certain very limited circumstances a specific visible wavelength (e.g. 532 nm from a frequency-doubled Nd:YAG laser) can be obtained with a single such process, typically several such processes are required in order to obtain an arbitrary yet specific wavelength. Not only are such systems highly complicated to construct and maintain, but the parametric processes are not highly efficient. Therefore, cascading parametric processes often results in lower output power or places high requirements on the original pump laser input power and beam quality.
Thus, there is a need in the art for improved optical sources emitting in the visible and near-visible region.